LOS ANGELES — There’s a lot more purging going on in this inevitable sequel to last summer’s surprise horror hit “The Purge.” Expanding the parameters of the low-budget original by taking the action literally out into the streets, “The Purge: Anarchy” efficiently exploits its high-concept premise while delivering far more visceral thrills than its predecessor. Like it or not, a new franchise seems to have been born.

Set ten years in the future, the film written and directed by James DeMonaco (repeating his chores from the original) again takes place during the annual Purge, a government-sanctioned 12-hour period in which ordinary citizens are allowed to commit heinous crimes with no fear of punishment. Created as a way to allow people to indulge their basest instincts so as to keep the crime rate down the rest of the year, participants are urged to “have a good cleanse” while those seeking shelter from the nihilistic mayhem are constantly advising each other to “stay safe.”

The latter is exactly what most of the featured main characters are trying to do, including single mother Eva (Carmen Ejogo), her feisty 16-year-old daughter Cali (Zoe Soul) and bickering married couple Shane (Zach Gilford) and Liz (Kiele Sanchez). The exception is Leo (Frank Grillo), a loner who, outfitted with an armor-plated car and loads of weaponry, heads out into the night for reasons of his own.

For contrived reasons too convoluted to explicate, Leo becomes the reluctant and unlikely protector of the other four when they find themselves trapped outside during the violence-filled night. Not only must they avoid the various ordinary citizens participating in the mayhem, including a scarily masked gang of young miscreants, but also the groups of black uniform-clad paramilitary types who massacre victims with automatic weapons from the backs of huge trucks. After Leo’s car becomes disabled, the group is forced to make their way on foot through the mean streets to the safe home of Eva’s employer.

While the first film was essentially an elaborate home invasion thriller, this follow-up more closely resembles a John Carpenter-style action movie (DeMonaco scripted the “Assault on Precinct 13” remake) with its plethora of well-staged, ultra-violent set pieces. And while character development is clearly not a high priority, the principal figures are a generally engaging and sympathetic lot, with Grillo’s steely Leo particularly intriguing.

More interestingly, the film expands on the original premise by introducing racial and class-conscious themes into the storyline: Eva’s elderly father (John Beasley) is seen sacrificing himself in one of the more wickedly clever plot twists; a Black Panther-style group led by a firebrand insurgent (Michael K. Williams of “The Wire”) violently rebels against the Purge; and the desperate quintet become would-be prey to a group of wealthy white people who have bid at an auction for the privilege of hunting them down.

While the film would have gained resonance if these provocative ideas had been developed more fully, it works well enough on its own terms, with Grillo’s commanding turn anchoring the proceedings. Director DeMonaco fills the screen with arresting images — a flame-engulfed bus seen barreling down the street in the background is particularly haunting — and keeps the pacing brisk enough to prevent dwelling on the plot contrivances. Effectively adding to the tense atmosphere is Nathan Whitehead’s excellent electronic music score.